Field of the Invention
The present disclosure relates to methods for producing biodiesel, and more particularly, to a method for producing biodiesel from non-edible oils.
Description of Related Art
Biodiesel is a re-generable fuel for replacing diesel. The molecules in biodiesel are primarily fatty acid methyl esters (FAMEs) usually obtained from trans-esterification of oils. Rapid alkali-catalyzed chemical processes with high yields are mainly used for the commercial productions of biodiesel. However, such processes are operated at high temperature and pressure, which are extremely energy consuming. The processes also have various drawbacks, such as saponification, difficulties in recycling the glycerol byproduct, the need to remove residual salts, and the productions of large amounts of effluent, which lead to environmental pollution. Therefore, as compared with the chemical processes for producing biodiesel, the processes for producing biodiesel by enzymatic catalysis under moderate conditions are regarded as environmentally friendly processes.
The conventional processes for producing biodiesel often require expensive refined oils as raw material, such as soybean oil, rapeseed oil, cottonseed oil and sunflower oil. The oil raw material for producing biodiesel takes up 85% or more of the production cost. These processes are extremely costly to the developing countries with shortage of such edible oil. Hence, the use of non-edible oil in the production of biodiesel contributes significantly to the economy and environmental protection.
Current researches have found that some enzymatically catalyzed processes in producing biodiesel can utilize low cost non-edible oil. For example, Abulla et al. (Rev. Biotechnol. 31, 53-64. 2011) and You et al. (Bioresour. Technol. 148, 202-207. 2013) found that various types of lipases from different bacterial strains can convert Jatropha oil into biodiesel. However, those researches all used immobilized lipases. Although the immobilization of enzymes improves the enzyme stability and leads to easy separation of products and repeated uses of enzymes, its expensive cost is unfavorable for industrial production.
Candida rugosa lipase (CRL) is a commercially available enzyme with an extremely wide range of applications. Various lipase isomers (i.e., isozymes) can be isolated from commercially available crude CRL. However, five C. rugosa genes encoding lipase with different expression levels have currently been identified, and the amino acid sequences encoding the five genes have high homology. As such, it is difficult to directly purify each of the isozymes from the C. rugosa culture in the industrial application scale. Moreover, C. rugosa translates its CTG codon into serine, such that the recombinant CRL isozymes expressed in a typical host cell (which translates the CTG codon into leucine) become non-functional.
In light of the drawbacks in the above conventional technologies, the present disclosure hereby provides a method for producing biodiesel with high yield using a recombinant yeast lipase to resolve the drawbacks.